A major objective of this project concerns the genetic organization of the bacterium Escherichia coli and mechanisms by which this organization can be altered. Of particular interest is the nature, distribution, and importance of repeated sequences in the chromosome. For example, ribosomal RNA and some tRNA species are coded by several identical structural genes; these redundant genes may be either clustered or scattered throughout the chromosome. In addition, a new class of genetic elements, called insertion sequences, has been discovered; these insertion sequences also occur repeatedly in the E. coli chromosome. Previous research from this laboratory has shown that uneven recombination between the repeated ribosomal RNA genes can lead to large tandem duplications. These duplications are notable because of the high frequency of their occurrence and because genetic duplications are thought to provide a reservoir of extra genetic material which could be altered through evolutionary processes. These studies are being extended to other chromosomal rearrangements, with emphasis being placed on the involvement of repeated genes and possibly of insertion sequences on their generation. Another major focus of research concerns the genetics, structure and function of glycine tRNA. Of particular interest is the structure and expression of the tRNA (superscript Gly, subscript GGG) structural gene, glyU.